Liquid metal heat exchangers with pressure absorbing means

ABSTRACT

Heat exchangers of the type using liquid sodium as a heat exchange fluid contain chambers inside their casings which are susceptible of collapse and/or breakage for the purpose of limiting the consequences of a reaction of sodium with water and steam in case of damage or failure to the means separating the two fluids.

United States Patent Inventors Sergio Bruschetti Via T. Tasso 9/8, Savona;

Ennio Zummo, Via Dagnino 38/3, Genoa- Pegli, both of Italy Appl. No. 853,734 Filed Aug. 28, 1969 Patented Oct. 19, 1971 Priority Sept. 25, 1968 Italy LIQUID METAL HEAT EXCHANGERS WITH PRESSURE ABSORBING MEANS 12 Claims, 10 Drawing Figs.

US. Cl 165/ 134, 176/37 Int. Cl F28f 19/00 i501 FiilTiFeZihIf..I.Ili :TTF/MHT,

[56] References Cited UNITED STATES PATENTS 3,205,146 9/1965 Hackney et al. 176/38 X 3,398,789 8/1968 Wolowoduik et a1 165/134 3,423,286 1/1969 Weems et a1. 176/37 Primary Examiner-Frederick L. Matteson Assistant ExaminerTheophil W. Streule Attorney-McGlew & Toren ABSTRACT: Heat exchangers of the type using liquid sodium as a heat exchange fluid contain chambers inside their casings which are susceptible of collapse and/or breakage for the purpose of limiting the consequences of a reaction of sodium with water and steam in case of damage or failure to the means separating the two fluids.

LIQUID METAL I-IEAT EXCHANGERS WI'I'II PRESSURE ABSORBING MEANS BACKGROUND OF INVENTION The present invention is directed to steam generators (or superheaters) using a liquid metal as the heat transfer medium, of the type containing a plurality of pipes with vertical straight pipes within an elongated cylindrical body having heads arranged at its ends, and a rupturable diaphragm disposed between the exterior of the body and a covering gas chamber located within its interior. In such generators highpressure water and steam passes through the pipes while liquid sodium flows over the pipes. Steam generators of the type having wormlike or helical pipes inserted forklike in a single upper head and with a coaxial cylindrically shaped central free space, are somehow similar, as their uses, to the previous type and thus are not shown.

On the contrary, an example is shown of another type of steam generator with a nest of flat sinuous or wormlike pipe panels as an example of the general characteristics of the present disclosure.

SUMMARY OF INVENTION The object of the present invention is to avoid the disadvantages due to the sodium/water chemical reaction caused by damage or failure in the integrity of the means separating the sodium and water, such as when a leak develops in a pipe separating the sodium and water.

The main characteristic of the invention concerns inserting inside a cylindrical body casing at least one empty and sealed chamber capable of absorbing at least a part of the first pressure wave caused by the sodium/water reaction, through a deformation by deflection, and thus releasing the initial volume of the flash expansion hydrogen gas, produced by the reaction between sodium and steam, so as to allow the efiective intervention of the normal and emergency automatic system for adjustment and safety. 7

The main characteristics and requirements of the invention are represented by:

a collapsing deformation with sharp starting and complete development;

that the initial shape and size of the exchanger are not altered, so as not to alter the other portions of the exchanger during the collapse;

an efficiency extending for the whole section and length of the exchanger; and 3 a possibility and convenience of restoring the exchanger at least for some of the different solutions possible.

The collapsible bodies and elements may be partly jointed to other dismountable portions of the exchanger, or may be simply contained therein, in consequence thereof the useful cylindrical portion, obviously with circular section, may be complete or not; it may also contain a differently shaped portion for initiating the collapse, preestablished in the most favorable shape and direction; further, it may still incorporate the different portions in the form of rupturable diaphragms, for transferring the effects of the explosive reaction from the lower portion of the heat exchanger to the upper covering gas or to the exterior of the casing.

The collapsible bodies or elements may be arranged in the tube nest or in other useful areas encumbering the useful portion of the exchanger. n the contrary the collapsible body may be arranged in other portions, with a smaller increase or no increase at all in the required volume for the exchanger, and may also partly replace the interior structure of the heat exchanger which slows downs the thermal transmission between different zones of the exchanger. The location of latter possibility is adjacent the outside of cylindrical body and in the inner cylindrical shell, in its function as a separator between two inner zones through which the sodium passes at different temperature. The bodies may also be arranged conveniently in the axial portion of the exchanger which is free of pipes, when such portion is not used as a passage for the sodium.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment, and another general embodiment, of the invention are shown, by way of example only, by sections and diagrammatic views in the accompanying drawings.

FIG. 1 is a sectional view taken along the line l-I in FIG. 2, of a generic type of steam generator with a nest of pipe panels of sinuous form arranged for counter of reverse parallel and cross circulation, and with collapsible bodies arranged on the inner wall of the casing;

FIG. 2 is a cross-sectional view of the heat exchanger taken along line IIII of FIG. 1;

FIG. 3 is a half-sectional view, shown for cleamess sake without any reference numeral, of another embodiment of a steam generator incorporating the present invention;

FIG. 4 is a partial vertical sectional view of an undifferentiated collapse body coaxially arranged inside the tubular beam supporting the nest of pipe panels;

FIG. 5 shows a partial development of the wall of tubular beam in FIG. 4, FIGS. 4 and 5 show the application of the present invention to the generator shown in FIG. 3;

FIG. 6 is a variation of the arrangement illustrated in FIG. 4 and shown in partial vertical section the application of a collapse body provided with rupturable diaphragms for discharge into an upper chamber containing covering gas;

FIG. 7 is a partial development of the wall of the tubular beam shown in FIG. 6;

FIG. 8 shows a partial development of the tubular body with the rupturable diaphragms shown in FIGS. 6 and 7;

FIG. 9 is a reduced view taken along the line lX-IX of FIG. 8; and

FIG. 10 shows a partial vertical section of a modification of the collapse body provided with breakage diaphragms, but with discharge to the exterior of the steam generator.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1 and 2, casing l of the generator has a dismountable flange 3 to which an upper single head 2 is connected. The head 2 comprises a header or collector 5 for the outlet of superheated steam (arrow 6), a tubular element 8 for the connection of a rupturable diaphragm (not shown), and the elements (not shown) relating to the covering gas contained in a chamber 9 in the upper end of the casing. The flat worm or sinuous pipes or pipe panels I2, each comprises a downwardly extending inlet pipe II and a plurality of upwardly extending loops 13, the latter being the longest possible, and an upwardly extending outlet pipe 14. The inlet and outlet pipes II, 14 are connected to the respective inlet and outlet headers 5-7 and the pipe panels 12 are supported by pendular rods 16 anchored to the upper head 2. I

Hot sodium (arrow 17) is fed through tubular inlet branches 18 into the casing forming a free surface or liquid level 19, and is discharged (arrow 20) through the bottom tubular outlet branch 21 passing in reversed or counter and crossflow with respect to the passage of water and steam through the pipe panels 12.

The nest of pipe panels 12, which are opposite as shown in plan, has a shape of regular hexagon 24, and groins or segments 25. between the hexagon and the casing, house collapsible bodies 26 having a length 27 nearly equal to that of worm pipes 12.

The collapsible bodies consist of an inner thin wall 28, having a circular arcuate shape, connected to a strong outer support wall 29, also having a circular arcuate shape which is fixed to the casing I, so as to allow the relevant replacement.

FIG. 3 is a sectional view of a steam generator with the preferred shape and arrangement, which is the object of applicants' other patents, comprising no reference numeral for clearness sake, and showing a form of the original construction before the collapsible safety devices which are the object of the present invention are applied thereto.

In FIGS. 4 and 5, which still show the preferred type of applicants other patents, casing 4I, tube sheets plates 42-43. inlet branches 45 and outlet branches 47 for the sodium according to arrows 44-46, see FIG. 5, are arranged in the normal way. Vertically extending straight pipes 50 of a pipe bundle pass through plates 42-43 and terminate in elements 52-53 at suitable headers or collectors 54-55 for the water and steam, which are shown in FIG. 3 but not in FIGS. 4 and 5. The pipes 50 have in their upper part sinusoidal curve section 51 near their upper ends for accommodating any differential expansion. The free level 57 of the sodium is located above the inlet branch 45; and an upper chamber 49 above the level 57 contains an inert covering gas which can discharge to the outside through the tubular branch 48 and the gas rupturable diaphragms (see FIG. 3).

The pipes 50 are supported at regular intervals by grates 59-59 provided with through bores surrounding the support bores for the pipes to provide the parallel (counter or reverse) flow. The grates are welded to a heavy walled pipe 60 coaxial to casing 41 fixedly fastened at 62 to the lower pipe plate 43 and axially slidable at 63 in the upper pipe plate.

The pipe 60 is bored with holes 61 in a regular pattern for nearly its entire length and has, at its lower part, an extension 64 with a crosslike section, so as to allow the normal bottom discharge 65 and the emergency discharge through a branch 66 (see FIG. 3).

The collapsible chamber consists of a thin walled cylinder 70 closed by end members 71-72, end member 17 adjusted by a spring device 73 and end member 72 carried by a stationary support 74 in a depression or reduced pressure phase extended to the exchanger entire length.

The collapsible chamber is provided with short sector plates 76 which, without constituting a surrounding mechanical reinforcement, decrease the bypass losses of sodium from the pipe nest.

The mounting and replacement of the cylinder 70 forming the chamber occur through the top by cutting and welding again the closure member 56.

FIGS. 6, 7, 8 and 9 show a modification of the collapse chamber, while the other parts of the generator shown in FIG. 3 are unchanged.

The collapsible chamber consists of a cylinder 80, inserted within the pipe 60 which supports the carrying grates 58-59, sufiiciently strong and carrying at its lower end a rupturable diaphragm 81, other similar diaphragms 82 are fixed at calculated intervals along the cylindrical periphery of the cylinder 80 up to near the free level of the sodium. The upper portion of cylinder 80, corresponding to the chamber containing the covering gas, is provided with holes 84 in alignment with bores 85 through the pipe 60. The pipe 60 also contains bore 86 arranged adjacent to the rupturable diaphragms 82 to afford, in case one or more lower diaphragms 82 rupture, the highest freedom possible for discharge of the gases of the chemical reaction and flash of water into steam inside the casing containing the covering gas, taking advantage of its compressibility and the intervention of the existing outwards rupturable diaphragm.

The upper end 87 of cylinder 80 containing the diaphragms 81-82 is opened and kept open by an elastic crosslike element 89; in order to obviate the possible penetration of liquid sodium into the cylinder (which is harmful for the discharge through the diaphragms), is provided a catching pipe 88 which. made periodically in communication with a reduced pressure outside room, works as a bottom discharge of the cylinder.

The diaphragms mounted in cylinder 80, in normal working condition are not subject to pressure differences (except for the hydraulic board), while they are subject to a sharp increase of dynamic pressure at the initiation of the water reaction and for the time which the pressure wave takes in expanding in the sodium space outside the pipes, from the damaged zone to the free surface in the upper chamber containing the covering gas.

For such a function, it is advisable to have the rupturable diaphragms made of fragile material.

The mounting and replacement of cylinder occur through the top by cutting and welding again the closure member 56.

FIG. 10 shows another modification of the collapsible chamber with a discharge from pipe 90 to the exterior of the generator casing. The pipe 90 has a bottom diaphragm 91 and side diaphragm 92 which are of stronger construction and higher calibration, as they are always subject to the hydrostatic pressure of the sodium and the covering gas. The pipe 90 has no other bores, does not rest on the bottom, is sealingly fixed at the top by a welding 93 (which may be repeated after a possible replacement) to collar 94 of the upper pipe plate 42, and has an upper exterior branch extension 95 for the connection to the discharge piping.

The tubular beam 60 carrying the grates and pipe nest contains openings which correspond correspondingly to the breakage diaphragms 92.

Although for purposes of description the present invention has been based on the above-described arrangement and has been shown by way of example only, many modifications and changes may be made in embodying the invention, all of them however to be considered as based on the following claims,

We claim:

1. Heat exchangers of the type using liquid metal, such as liquid sodium, as a heat transfer medium comprises an upwardly extending casing closed at its ends and forming a pressure vessel, a plurality of pipes disposed within and extending upwardly through said casing, means for circulating the liquid metal through said casing for passage over said pipes and for forming a level of the liquid metal in the upper part of said casing and providing a space between the level of the liquid metal and the upper end of said casing for holding a covering gas, means for circulating a fluid through said pipes in indirect heat exchange relationship with the liquid metal, wherein the improvement comprises means positioned within said casing with at least a portion thereof located below the level of the liquid metal for absorbing at least in part the initial pressure wave generated within said casing when due to leakage or other failure there is direct contact between the liquid metal and the fluid in said pipes, said means comprising walls forming a hollow longitudinally extending member with at least a portion of the exterior surface thereof in contact with the liquid metal and having a portion of said walls thereof substantially coextensive with said upwardly extending pipes and subject to fail by absorbing an increase in pressure, and means for replaceably mounting and supporting said member in said casting separate from said pipes.

2. Heat exchangers, as set forth in claim 1, wherein said walls forming the hollow longitudinally extending member comprise a longitudinally extending support wall and a deflectable wall secured to and disposed in coextending relationship with said support wall and forming with said support wall a laterally enclosed space, said deflectable wall having a reduced thickness and strength relative to said support wall and being oriented toward the liquid metal flowing over said pipes, whereby the strength of said deflectable wall is selected so that it is arranged to collapse when it is exposed to the pressure generated in a reaction between the liquid metal and the fluid flowing in the pipes.

3. Heat exchangers, as set forth in claim 2, wherein said walls forming the longitudinally extending member comprising an upper end closure and a lower end closure secured to said support and deflectable walls for forming a sealed chamber, and said sealed chamber having a reduced pressure therein relative to the pressure contacting the exterior of said chamber.

4. Heat exchangers, as set forth in claim 3, wherein said pipes arranged within said casing in an upwardly extending polygonally shaped bundle, the inner surface of said casing spaced outwardly from said pipes located about the exterior of the bundle of said pipes, and said sealed chamber being located within the space between said pipes and said casing with said deflectable wall facing inwardly toward said pipes.

5. Heat exchangers, as set forth in claim 1, wherein an upwardly extending tubular member disposed within and in coaxial relationship with said casing, said tubular member located centrally within the pipes in said casing, said walls forming the hollow longitudinally extending member spaced within and from said tubular member, said hollow longitudinally extending member being removably mounted within said tubular member, the portion of said tubular member located below the level of the liquid metal in said casing having a plurality of holes therethrough for affording contact between the liquid metal and the exterior surface of said hollow member within said tubular member.

6. Heat exchangers, as set forth in claim 5, wherein a plurality of upwardly spaced annular collars secured to and extending between said tubular member and said hollow member for blocking flow of liquid metal through the space between said tubular member and hollow member to prevent the liquid metal from bypassing around said pipes.

7. Heat exchangers, as set forth in claim 5, wherein said tubular member having openings therethrough above the level of the liquid metal communicating between the interior of said tubular member and the space above the level of the liquid metal.

8. Heat exchangers, as set forth in claim 5, wherein said walls forming said hollow member comprising a cylindrically shaped thin walled section sealed at its upper and lower ends and said thin wall section selected to collapse when exposed to the pressure generated by the liquid metal-fluid reaction.

9. Heat exchangers, as set forth in claim 5, wherein said walls forming said hollow member comprising a cylindrically shaped section open at its upper end, a rupturable diaphragm in the lower end of said section, a plurality of rupturable diaphragms fitted in openings in said section below the level of the liquid metal and arranged opposite the openings in said tubular member, and said tubular member and said section having aligned openings therethrough above the level of the liquid metal in said casing.

10. Heat exchangers, as set forth in claim 9, wherein a upwardly extending pipe located within said hollow member and having its lower end located closely above the lower end of said hollow member, and said pipe extending upwardly from said hollow member and said casing whereby the upper end of said pipe can be secured to a reduced pressure chamber for removing from said hollow member any liquid metal which enters said hollow member through its open upper end.

11. Heat exchangers, as set forth in claim 5, wherein said hollow member extending upwardly from the upper end of said tubular member and projecting outwardly from the upper end of said casing, said hollow member being integrally attached to said casing adjacent its upper end, whereby the upper end of said hollow member is arranged to be connected to discharge piping.

12. Heat exchangers, as set forth in claim I, wherein said pipes comprising a plurality of individual pipe panels, each said pipe panel comprising an upwardly extending inlet extending from the upper end of said casing to the lower end of said pipe panels within said casing, an outlet conduit extending downwardly from the upper end of said casing to the upper end of said pipe panel and a sinuously shaped pipe section extending from said inlet conduit to said outlet conduit comprising a multiplicity of horizontally disposed pipe sections interconnected by upwardly extending pipe loops. 

1. Heat exchangers of the type using liquid metal, such as liquid sodium, as a heat transfer medium comprises an upwardly extending casing closed at its ends and forming a pressure vessel, a plurality of pipes disposed within and extending upwardly through said casing, means for circulating the liquid metal through said casing for passage over said pipes and for forming a level of the liquid metal in the upper part of said casing and providing a space between the level of the liquid metal and the upper end of said casing for holding a covering gas, means for circulating a fluid through said pipes in indirect heat exchange relationship with the liquid metal, wherein the improvement comprises means positioned within said casing with at least a portion thereof located below the level of the liquid metal for absorbing at least in part the initial pressure wave generated within said casing when due to leakage or other failure there is direct contact between the liquid metal and the fluid in said pipes, said means comprising walls forming a hollow longitudinally extending member with at least a portion of the exterior surface thereof in contact with the liquid metal and having a portion of said walls thereof substantially coextensive with said upwardly extending pipes and subject to fail by absorbing an increase in pressure, and means for replaceably mounting and supporting said member in said casting separate from said pipes.
 2. Heat exchangers, as set forth in claim 1, wherein said walls forming the hollow longitudinally extending member comprise a longitudinally extending support wall and a deflectable wall secured to and disposed in coextending relationship with said support wall and forming with said support wall a laterally enclosed space, said deflectable wall having a reduced thickness and strength relative to said support wall and being oriented toward the liquid metal flowing over said pipes, whereby the strength of said deflectable wall is selected so that it is arranged to collapse when it is exposed to the pressure generated In a reaction between the liquid metal and the fluid flowing in the pipes.
 3. Heat exchangers, as set forth in claim 2, wherein said walls forming the longitudinally extending member comprising an upper end closure and a lower end closure secured to said support and deflectable walls for forming a sealed chamber, and said sealed chamber having a reduced pressure therein relative to the pressure contacting the exterior of said chamber.
 4. Heat exchangers, as set forth in claim 3, wherein said pipes arranged within said casing in an upwardly extending polygonally shaped bundle, the inner surface of said casing spaced outwardly from said pipes located about the exterior of the bundle of said pipes, and said sealed chamber being located within the space between said pipes and said casing with said deflectable wall facing inwardly toward said pipes.
 5. Heat exchangers, as set forth in claim 1, wherein an upwardly extending tubular member disposed within and in coaxial relationship with said casing, said tubular member located centrally within the pipes in said casing, said walls forming the hollow longitudinally extending member spaced within and from said tubular member, said hollow longitudinally extending member being removably mounted within said tubular member, the portion of said tubular member located below the level of the liquid metal in said casing having a plurality of holes therethrough for affording contact between the liquid metal and the exterior surface of said hollow member within said tubular member.
 6. Heat exchangers, as set forth in claim 5, wherein a plurality of upwardly spaced annular collars secured to and extending between said tubular member and said hollow member for blocking flow of liquid metal through the space between said tubular member and hollow member to prevent the liquid metal from bypassing around said pipes.
 7. Heat exchangers, as set forth in claim 5, wherein said tubular member having openings therethrough above the level of the liquid metal communicating between the interior of said tubular member and the space above the level of the liquid metal.
 8. Heat exchangers, as set forth in claim 5, wherein said walls forming said hollow member comprising a cylindrically shaped thin walled section sealed at its upper and lower ends and said thin wall section selected to collapse when exposed to the pressure generated by the liquid metal-fluid reaction.
 9. Heat exchangers, as set forth in claim 5, wherein said walls forming said hollow member comprising a cylindrically shaped section open at its upper end, a rupturable diaphragm in the lower end of said section, a plurality of rupturable diaphragms fitted in openings in said section below the level of the liquid metal and arranged opposite the openings in said tubular member, and said tubular member and said section having aligned openings therethrough above the level of the liquid metal in said casing.
 10. Heat exchangers, as set forth in claim 9, wherein a upwardly extending pipe located within said hollow member and having its lower end located closely above the lower end of said hollow member, and said pipe extending upwardly from said hollow member and said casing whereby the upper end of said pipe can be secured to a reduced pressure chamber for removing from said hollow member any liquid metal which enters said hollow member through its open upper end.
 11. Heat exchangers, as set forth in claim 5, wherein said hollow member extending upwardly from the upper end of said tubular member and projecting outwardly from the upper end of said casing, said hollow member being integrally attached to said casing adjacent its upper end, whereby the upper end of said hollow member is arranged to be connected to discharge piping.
 12. Heat exchangers, as set forth in claim 1, wherein said pipes comprising a plurality of individual pipe panels, each said pipe panel comprising an upwardly extending inlet extending from the upper end of said casing to the lower end of saId pipe panels within said casing, an outlet conduit extending downwardly from the upper end of said casing to the upper end of said pipe panel and a sinuously shaped pipe section extending from said inlet conduit to said outlet conduit comprising a multiplicity of horizontally disposed pipe sections interconnected by upwardly extending pipe loops. 